The ISO setting controls your camera’s sensitivity to light. Most cameras have a variety of exciting choices for this, including:

Auto

100

200

400

800

Of course, the number of choices on your camera will probably vary from my list. It may have more, maybe less; all depends on what the manufacturer thought your sensor could handle. The big question is:

What do these numbers do?

It’s actually pretty easy – The higher the number, the less light you need to get a photo (and the further your flash will go). The lower the number, the more light you need (and your flash distance will decrease).

After reading the above, you’re probably wondering why you wouldn’t just stick it at the highest setting and be done with it. Ahh, that’s the other side of the coin.

The higher the settings, the more “noise” you pick up (we’re talking photographic noise, not the kind your two year old makes when it bed time). In fact, at their highest setting, some cameras produce such ridiculous levels of noise the photos are almost worthless. They look like someone sprinkled little specks of red, green, and blue glitter all over ‘em. For more on noise and how to prevent it, try:

For the most part, I recommend keeping your camera on Auto ISO for general picture taking. Most cameras adjust the ISO for the best combination of low noise and hand-holdable shutter speed (so you don’t need a tripod). However, there are exceptions:

1. If you’re shooting with flash and your subject is far away. OK, we’re not talking a football field away – no amount of fiddling with your ISO will increase your flash distance enough for that. However, if your subject is a realistic distance away, you may want to consider overriding the camera’s “Auto” ISO setting. Manually adjust it to one of the higher settings and you’ll get a little more mileage out of your flash (most cameras shoot low ISO when flash and Auto ISO are engaged). For more on flash distance:

2. If you have a tripod. If you’re taking a photo using existing light and you have a tripod, you should manually adjust your ISO to the lowest settings. Most of the time, an Auto ISO selection will try to compensate for low light by cranking up the ISO. It wants to insure you have enough shutter speed to handhold the camera (It can’t tell you’re using a tripod). Since you don’t need any help keeping the camera steady, why put up with excess noise? Drop the ISO manually.

3. Action shots. If you’re shooting fast moving action, you may need to increase your ISO. Keep in mind the “Auto” ISO computer is trying to give you a good shutter speed to hand-hold the camera with, but it’s not necessarily trying to give you the camera’s top speed either. So, if you’re shooting race cars as they wiz by and find you’re just not “stopping” them, crank up the ISO a notch and see if it helps. You might also try switching to “Action” or “Sports” mode while you’re in there.

Sure, there’s bound to be other times you need to change the ISO, but those three are the most common I run across. Just remember, the higher you set your ISO, the more noise you’re images will pick up.